Research into OTFTs has gained great interest because of their potential applications in low cost and large area flexible electronics. These include driving circuits for future all-organic OLED-based flat panel displays, plastic RF-ID circuits, gas sensors, and chemical sensors.
The most common gate dielectric in organic OTFTs is a thermally-grown silicon oxide (SiO2) on crystalline silicon. However, for low-cost, all-plastic, and large-area applications the use of thermally grown SiO2 is not of particular interest. A solution-processable gate dielectric is the most attractive alternative as it can be easily prepared by spin coating, casting, or printing at low temperature and under ambient conditions.
Various solution-processable gate dielectrics have been used in the past. These include poly-4-vinylphenol (PVP), polymethyl methacrylate (PMMA), poly vinyl alcohol (“PVA”), benzocyclobutene (“BCB”), polyimide (“PI”), and self-assembled monolayers. OTFTs using a polymer dielectric operate at high voltages due to low dielectric constant (k) values. Therefore, inorganic oxides such as TiO2, Ta2O5, and Al2O3 are used as they have higher k values and thus the operating voltages can be reduced. However, inorganic oxides require fabrication techniques such as anodic oxidation, magnetron sputtering, and electron-beam evaporation. This makes the deposition process and consequential device fabrication relatively difficult and expensive. It is therefore desirable to have solution-processable inorganic dielectrics for low operating voltage OTFTs.